This invention relates to polyester fiber having an improved balance of fiber properties including dyeability, light stability, dye lightfastness, and boiling water shrinkage.
Polyester fibers have been prepared for commercial use for more than thirty years, and are produced in large quantities. Most commercial polyester comprises poly(ethylene terephthalates).
The term "fiber" as used herein includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple). The term "yarn", as used herein, means a continuous strand of fibers.
Because fibers produced from polyester have a number of outstanding characteristics: excellent dimensional stability and sturdiness, a high degree of crease resistance, good bulk elasticity, and warm handle, the fibers have found a wide variety of applications, especially in the textile field.
In the past, in order to produce polyester fibers having excellent dyeability, i.e., dark dyed polyester fibers, various chemical additives or modifiers have been employed. A problem associated with the use of these additives or modifiers is that many times they reduce the light stability and dye lightfastness of the resulting fibers.
Another procedure used in the past for producing polyester fibers having excellent dyeability is to produce fibers with high long-period spacing (LPS). A problem associated with fibers produced by this procedure is that, many times, dimensional stability is decreased, which results in high shrinkage of the fibers.
Thus, the combined objective of polyester fibers having excellent dyeability along with good thermal stability and lightfastness become somewhat irreconcilable in many of the commercial processes for producing polyester fibers.
For many commercial applications, it is necessary that polyester fibers must have good thermal stability, i.e., relatively low shrinkage over a large temperature range. While the maximum permissible shrinkage will vary depending on the intended use of the fibers, in many home furnishing and automobile applications, such as body cloth and fabrics containing different yarns in adjacent areas of the same fabric, it is desirable that the fibers of the yarns have a boil-off shrinkage of less than twelve percent (12%).
The present invention provides polyester yarn containing fibers having an improved combination of properties with a darker dyeing capability, good thermal dimensional stability, and good light stability, dye lightfastness, and a method of their preparation which results in a fiber having an overall better combination of properties, i.e., one which involves less sacrifice of one or more individual properties to improve the other.
It has been unexpectedly discovered that yarn comprising poly(ethylene terephthalate) fibers having the above-described combination of properties can be prepared from a partially oriented feeder yarn comprising poly(ethylene terephthalate) fibers having a birefringence (.DELTA.n) of at last 0.0175 by drawing the feeder yarn at controlled temperatures and draw ratios, annealing the drawn yarn at controlled temperatures, and subsequently drawing, a second time, the annealed yarn at controlled temperatures and draw ratios.
The poly(ethylene terephthalate) fibers of the yarn which have been produced by this procedure are characterized by a long-period spacing (LPS) of over 200 .ANG., an average crystal size of in the range of from about 30 to about 45 .ANG., and crystallinity of less than 24 percent.